When animals are put on pasture, some are more susceptible to parasitism than others. The parasite control programme will vary depending on their age and level of immunity.
are very susceptible to parasites in their first grazing season. The parasite burden in the animal can impact animal performance and even result in diseases (diarrhoea, death). A treatment during the grazing season is usually necessary.
diagnostics should be considered. Treatment may or may not be indicated. If no treatment is given at the start of the grazing season, cattle should be monitored closely and further diagnostics done later in the season.
adult cattle develop acquired immunity against some parasites. Nevertheless, the impact of parasite burden should be monitored though diagnostics and treatment administered accordingly.
The development of immunity is progressive. When established, it helps in:3
A sufficient time of effective contact4 (TEC) with the infective larvae of parasites is necessary to build up immunity, before the first calving. In cattle, eight months is considered an adequate TEC.
A sustainable approach involves the correct use of anti-parasitics: the right dose, the right product, the right time and on the right animals. Historically it was common to worm the entire herd. Blanket deworming of all animals results in increased anti-parasitic resistance.
Strategic treatment – plan the treatment of groups of animals based on previous experience/history to minimise worm burden, pasture contamination and disease (can be part of refugia strategy).
Targeted treatment (TT) – treatment of groups of animals based on assessment of current parasite risk (e.g. treating at first grazing season when FEC indicates it) (can be part of refugia strategy).
Targeted selective treatment (TST) – treatment of individuals or subgroups based on an assessment of current parasite risk (e.g. treating only poorer doing calves). Often discussed is leaving a small proportion of animals untreated (can be part of refugia strategy).
Therapeutic treatment – treatment in response to clinical disease.